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6610-l11--1 - Wireless Scheduling 1 Puzzle Which direction...

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1 Wireless Scheduling
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2 Puzzle Which direction is white playing?
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3 Generic Wireless FS Model Error free service Lead/lag/in-sync Compensation model Channel monitoring and prediction
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4 Instantiations Channel state dependent packet scheduling (CSDPS) Idealized wireless fair queuing (IWFQ) Wireless packet scheduling (WPS) Channel-condition independent fair queuing (CIFQ) CBQ-CSDPS Server based fairness approach (SBFA) Wireless fair service (WFS)
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5 CIFQ STFQ (Start time fair queuing) used for the error free service Lag or lead computed as the difference between the actual service and the error free service A backlogged leading flow relinquishes slot with a probability p, a system parameter A relinquished slot is allocated to the lagging flow with the maximum normalized lag
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6 CIFQ (Contd.) In-sync flows not affected since lagging flows use slots given up by leading flows Lagging flows can still starve leading flows under pathological scenarios Provides both short-term and long-term fairness
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7 CBQ-CSDPS Same as IWFQ except that no explicit error free service is maintained Rather, lead/lag is measured based on the actual number of bytes s transmitting during each time window A flow with normalized weight r is leading if it has received channel allocation in excess of s*r, and lagging if it has received channel allocation less than s*r Lagging flows are allowed precedence
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8 CBQ-CSDPS Same problem as in IWFQ – lagging flows given precedence, and hence can capture channel Short term fairness is thus not guaranteed Additionally, leads and lags are computed not based on error-free service, but based on a time window of measurement … performance sensitive to the time window
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9 SBFA Any error free service model can be used SBFA reserves a fraction of the channel bandwidth statically for compensation by specifying a virtual compensation flow When a flow is unable to use a slot, it queues a slot- request to the compensation flow Scheduler serves compensation flow just as other flows When the compensation flow gets a slot, it turns the slot over to the flow represented by the head-of-line slot- request
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10 SBFA (Contd.) Compensation Flow of weight w Scheduled to Tx  Cannot transmit  because of error Slot queued into compensation flow Slot scheduled for Tx and handed over to F1 F1
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11 SBFA (Contd.) No concept of a leading flow All bounds supported by SBFA are only with respect to the remaining fraction of the channel bandwidth Performance of SBFA is sensitive to the statically reserved fraction No short-term fairness Long-term fairness dependent upon the reserved fraction
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12 Wireless Fair Service Uses an enhanced version of WFQ in order to support delay-bandwidth decoupling Lag of a flow incremented only if there is a flow that can use the slot Both lead and lag are bounded by per-flow parameters
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